Optical spectrometers collect and process light radiated from a sample to measure wavelength-specific properties of the sample. Typically, a spectrometer includes a collection/filter system, a grating, and a detector array. The collection/filter system captures a percentage of the light radiated from the sample and spatially filters the collected light. The grating spatially shifts different wavelength components of the incident light to different areas of the detector array, while detectors in the detector array convert sensed light to an electrical output signal. Processing electronics connected to the detector array quantify wavelength-specific properties of the sample based on the output signals from the detector array.
Conventional collection/filter systems typically use collection optics and a separate spatial filter, such as a pinhole or slit. Size constraints imposed on the optical spectrometer and components within the optical spectrometer necessarily limit the numerical aperture of the collection optics. Because the amount of radiated sample light collected by the collection optics is directly related to the numerical aperture, these size constraints also necessarily limit the collection efficiency of the collection optics. Further, the combination of the collection optics with the spatial filter places strict optical and mechanical requirements on the design of the optical spectrometer. Therefore, there remains a need for alternative collection/filter systems for use in optical spectrometers.